Trim Terminology
Interior window molding does double duty, covering gaps while defining a style.
Use this guide to understand what each part does and how all the pieces fit together.
The Crown
a) crown molding
Angles out from wall at top of window, adding dimension lacking in flat stock. Together with frieze board and cap, makes up entablature, a feature found in classical house styles, such as Georgian, Federal, and Greek Revival.
b) mitered return
Covers end grain as it carries profile to wall.
c) frieze board
Serves as base for attaching crown molding and cap. Its ends line up with outside edges of casing.
The Top Corner
d) crosshead strip
Provides transition between head casing and frieze board.
e) mitered return
Covers end grain as it carries profile to wall.
The Side Casing
f) side casing
Covers gap between side of window frame and wall.
g) backband molding
Adds depth and width to outside edges of casing. L-shaped to fit neatly over corners.
h) inside stop
Holds sash in window opening. Removing stops allows sash to be taken out for repair.
The Bottom Corner
i) horn
Extends stool past casing and apron by 1 to 2 inches.
j) mitered return
The Windowsill
k) stool
Hides gap between bottom edge of lower sash and top of windowsill outside.
l) apron
Provides visual support for stool. Ends line up with outside edges of casing. Aprons with a profile require mitered returns.
The Top
m) cap
Covers top of crown.
n) head casing
Covers gap between top of window frame and wall.
The Square Cut Miter
In many Victorian-era, Craftsman, and Colonial Revival homes, casing ends are cut square, then butted against either adjacent casing edges or corner rosettes, which are separate blocks slightly thicker and wider than casing stock. For this joint to work, casings must be symmetrical, not tapered.
o) rosette
p) square-cut joint